This invention relates to an electronic circuit and, in particular, to an electronic circuit comprising an integrated circuit having a power supply terminal, a noise filter disposed around the integrated circuit, a printed circuit having a pattern for supply a power supply to the power supply terminal of the integrated circuit through the noise filter.
In recent years, information electronic instruments such as portable telephone sets are widely used in the world. It is well known in the art that technique in digital circuits are used in the information electronic instruments.
The technique of digital circuits are important techniques for supporting an information technology (IT) industry. Recently, the technique of digital circuits such as a large-scale integrated circuit (LSI) is used not only in computers and communication related instruments but also in home electrical appliances and on-vehicle equipment.
When the LSI is operated, it well known in the art that a high frequency current generates on a power supply line of the LSI. The high frequency current dose not stay in the vicinity of the LSI, spreads in a wide area in a mounted circuit board such as a printed circuit board, inductively couples to signal wires or ground wires, and leaks from a signal cable as an electromagnetic wave.
The high frequency current not only causes a malfunction of its own instrument but also has an effect on other instruments and it results in causing electromagnetic compatibility (EMC).
In order to device a countermeasure, to separate the LSI serving as a generating source of a high frequency current from a power supply at a high frequency, namely, a method of power supply decoupling is effective. In prior art, a noise filter such as a bypass capacitor has been used as a decoupling element. Although an operating principle of the power supply decoupling is simple and clear, development of a noise filter having a low impedance coping with a high speed of the LSI falls behind drastically. Specifically, it is difficult to maintain the low impedance up to a high frequency range caused by a self-resonance phenomenon of the capacitor.
Therefore, in a case where removal of electric noises using capacitors is carried out across a wider frequency band, different types of capacitors having different self-resonance frequencies such as an aluminum electrolytic capacitor, a tantalum capacitor, and a ceramic capacitor are disposed in the vicinity of the LSI.
However, a conventional electronic circuit is disadvantageous in that it is troublesome to select a plurality of noise filters used to remove electric noises having a wide frequency band. In addition, the conventional electronic circuit is also disadvantageous in that it has a large mounted area to dispose a plurality of different types of noise filters.
With high speed and high frequency of the LSI, generated noises have a wide band and a high frequency. A high performance noise filter required to remove such noises is desired.
Noise filters for use in a semiconductor device are well known in the art. For example, a noise filter is disclosed, for example, in Japanese Unexamined Patent Publication Tokkai No. 2001-185,423 or JP-A 2001-185423. The noise filter disclosed in JP-A 2001-185423 comprises inductors inserted between respective signal ends and signal lines of the semiconductor device and capacitors connected between respective inductors and the ground.